In-ovo Delivery of Lipopolysaccharide Induces Protective Antiviral Responses Against Infectious Laryngotracheitis Virus Encountered Post-Hatch

Infectious laryngotracheitis virus (ILTV) is an avian respiratory virus that causes significant economic losses to the worldwide poultry industry. To address the limitations of current control measures against ILTV infections, it is crucial to develop novel measures that can complement or replace the existing control measures. The in-depth understanding of toll-like receptor (TLR)ligand interaction and activation mechanisms has facilitated the development of more specific synthetic ligands with therapeutic potentials capable of enhancing host immune responses against various infections. As a key ligand for activating the TLR4 signaling pathway, lipopolysaccharide (LPS) triggers immune responses against numerous pathogens. Previous research has demonstrated that the intramuscular injection of LPS in chickens can induce antiviral responses against low pathogenic avian influenza virus (AIV) infections. This study evaluated the potential of in-ovo delivery of LPS to stimulate innate antiviral responses against ILTV infection in post-hatch chickens. The results showed that in-ovo delivery of LPS at embryo day (ED)-18 significantly reduced mortality, clinical symptoms, and virus excretion in chickens infected with ILTV at day 1 post-hatch, which was associated with the expansion of the macrophage population in the lungs. This study provides a detailed understanding of the mechanisms underlying the antiviral responses elicited against ILTV infection following in-ovo delivery of LPS in chickens.